Work machine and method for controlling a work machine

Abstract

To smoothly start a power source in a working machine.SOLUTION: The work machine includes a power source, a hydraulic pump, a hydraulic brake, a brake charge valve, and a controller. The hydraulic pump is driven by the power source. The hydraulic brake generates a braking force by hydraulic oil discharged from a hydraulic pump. The brake charge valve controls a brake pump pressure indicating a hydraulic pressure of the hydraulic oil discharged from the hydraulic pump. The controller executes normal charge control for controlling the brake charge valve so that the brake pump pressure becomes a predetermined first pressure. When starting the engine, start auxiliary control for controlling the brake charge valve is executed so that the brake pump pressure becomes second pressure smaller than the first pressure.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to work machines and methods for controlling work machines. [Background technology]

[0002] Some work machines are equipped with a power source, a hydraulic pump, hydraulic brakes, and brake valves. For example, in the wheel loader disclosed in Patent Document 1, the hydraulic pump is driven by an engine as the power source. Hydraulic oil from the hydraulic pump is supplied to the hydraulic brakes via a brake valve. The brake valve is controlled in response to operation of the brake pedal. The hydraulic brakes are driven in response to operation of the brake pedal, thereby braking the front and rear wheels. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2011-80540 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, to improve energy efficiency in work machines, the capacity of hydraulic pumps has been increased to ensure a sufficient flow rate of hydraulic oil even when the rotational speed of the power source is low. Meanwhile, in such work machines, a load torque from the hydraulic pump acts on the power source. The larger the capacity of the hydraulic pump, the greater the load torque from the hydraulic pump. Therefore, when the power source is started, a large load torque acts on the power source, lengthening the time until the power source starts. An object of the present disclosure is to smoothly start the power source in a work machine. [Means for solving the problem]

[0005] A work machine according to one aspect of the present disclosure includes a power source, a hydraulic pump, a hydraulic brake, a brake charge valve, and a controller. The hydraulic pump is driven by the power source. The hydraulic brake generates braking force using hydraulic fluid discharged from the hydraulic pump. The brake charge valve controls the brake pump pressure, which indicates the hydraulic pressure of the hydraulic fluid discharged from the hydraulic pump. The controller executes normal charge control, which controls the brake charge valve so that the brake pump pressure becomes a predetermined first pressure. When starting the engine, the controller executes start assist control, which controls the brake charge valve so that the brake pump pressure becomes a second pressure lower than the first pressure.

[0006] A method according to another aspect of the present disclosure is a method for controlling a work machine. The work machine includes a power source, a hydraulic pump, a hydraulic brake, and a brake charge valve. The hydraulic pump is driven by the power source. The hydraulic brake generates braking force using hydraulic fluid discharged from the hydraulic pump. The brake charge valve controls a brake pump pressure that indicates the hydraulic pressure of the hydraulic fluid discharged from the hydraulic pump. The method includes performing normal charge control that controls the brake charge valve so that the brake pump pressure becomes a predetermined first pressure, and performing start assist control at engine start that controls the brake charge valve so that the brake pump pressure becomes a second pressure that is lower than the first pressure. [Effects of the Invention]

[0007] According to the present disclosure, when the power source is started, the brake pump pressure is suppressed to a second pressure, which is lower than the first pressure during normal charge control, by start-up assist control. As a result, the load torque from the hydraulic pump is reduced when the power source is started. This allows the power source to be started smoothly in the work machine. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a side view of a work machine according to an embodiment. [Figure 2]FIG. 2 is a schematic diagram showing a drive system for a hydraulic brake of a work machine. [Figure 3] FIG. 2 is an enlarged view of a portion of the configuration of a brake charge valve. [Figure 4] FIG. 4 is a diagram showing the characteristics of a brake charge valve. [Figure 5] 4 is a flowchart showing a process for controlling brake charge pressure. [Figure 6] 4 is a timing chart showing control of brake charge pressure. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a side view of a work machine 1 according to an embodiment of the present disclosure. The work machine 1 according to this embodiment is a wheel loader. As shown in Fig. 1, the work machine 1 includes a vehicle body 2, a work implement 5, and a traveling device 6.

[0010] The vehicle body 2 includes a front vehicle body 3 and a rear vehicle body 4. The rear vehicle body 4 is connected to the front vehicle body 3 so as to be able to swing left and right. A driver's cab 7 and a power compartment 8 are arranged in the rear vehicle body 4. The work equipment 5 is movably connected to the vehicle body 2. The work equipment 5 is used for work such as excavation. The work equipment 5 is attached to the front vehicle body 3. The work equipment 5 includes a boom 11, a bucket 12, and a work equipment actuator 13. The work equipment actuator 13 is, for example, a hydraulic cylinder. The work equipment 5 is operated by the work equipment actuator 13.

[0011] The traveling device 6 is attached to the vehicle body 2. The traveling device 6 causes the work machine 1 to travel. The traveling device 6 includes front wheels 16 and rear wheels 17. The front wheels 16 are rotatably supported by the front vehicle body 3. The rear wheels 17 are rotatably supported by the rear vehicle body 4. Note that in the drawings, only one of the left and right front wheels 16 and only one of the left and right rear wheels 17 are shown.

[0012] The work machine 1 is equipped with an engine 18 and a transmission 19. The engine 18 is the power source of the work machine 1 and is arranged in the power chamber 8. The transmission 19 is, for example, a hydrostatic continuously variable transmission. Alternatively, the transmission 19 may be a mechanical transmission including a plurality of speed change gears and a clutch. The transmission 19 transmits driving power from the engine 18 to the traveling device 6. This drives the front wheels 16 and rear wheels 17, causing the work machine 1 to travel.

[0013] The work machine 1 is equipped with hydraulic brakes 21, 22. The hydraulic brakes 21, 22 include a front brake 21 and a rear brake 22. The front brake 21 brakes the front wheels 16. The rear brake 22 brakes the rear wheels 17. FIG. 2 is a schematic diagram showing a drive system for the hydraulic brakes 21, 22. As shown in FIG. 2, the work machine 1 is equipped with a hydraulic pump 23, a hydraulic circuit 24, a brake charge valve 25, a brake valve 26, accumulators 27, 28, and a controller 29.

[0014] The hydraulic pump 23 is connected to the engine 18. Driven by the engine 18, the hydraulic pump 23 discharges hydraulic oil to a hydraulic circuit 24. The hydraulic circuit 24 connects the hydraulic pump 23 with the hydraulic brakes 21, 22. The hydraulic oil discharged from the hydraulic pump 23 passes through the hydraulic circuit 24 and is supplied to the hydraulic brakes 21, 22. The hydraulic brakes 21, 22 generate braking force using the hydraulic oil discharged from the hydraulic pump 23.

[0015] The brake charge valve 25 is disposed in the hydraulic circuit 24 between the hydraulic pump 23 and the brake valve 26. The brake charge valve 25 controls the brake pump pressure of the hydraulic pump 23. The brake pump pressure indicates the hydraulic pressure of the hydraulic oil discharged from the hydraulic pump 23. The brake charge valve 25 controls the brake pump pressure, thereby controlling the brake charge pressure of the accumulators 27, 28. The brake charge pressure indicates the hydraulic pressure of the hydraulic oil charged to the accumulators 27, 28.

[0016] The brake charge valve 25 is electrically controlled by a controller 29. The brake charge valve 25 controls the brake pump pressure in response to a command signal from the controller 29. The configuration of the brake charge valve 25 will be described in detail later.

[0017] The accumulators 27, 28 are connected to the hydraulic circuit 24 between the brake charge valve 25 and the brake valve 26. The accumulators 27, 28 are capable of storing a brake charge pressure large enough to operate the hydraulic brakes 21, 22 multiple times. The accumulators 27, 28 include a first accumulator 27 and a second accumulator 28. The first accumulator 27 stores the brake charge pressure for the front brake 21. The second accumulator 28 stores the brake charge pressure for the rear brake 22.

[0018] The hydraulic circuit 24 includes a first brake drive circuit 31 and a second brake drive circuit 32. The first brake drive circuit 31 is connected to the front brake 21. The first accumulator 27 is connected to the first brake drive circuit 31. The second brake drive circuit 32 is connected to the rear brake 22. The second accumulator 28 is connected to the second brake drive circuit 32.

[0019] The brake valve 26 is disposed in the hydraulic circuit 24 between the hydraulic pump 23 and the hydraulic brakes 21, 22. The brake valve 26 is connected to a first brake drive circuit 31 and a second brake drive circuit 32. A brake operating member 33 is connected to the brake valve 26. The brake operating member 33 can be operated by an operator to actuate the hydraulic brakes 21, 22. The brake operating member 33 is, for example, a pedal. Alternatively, the brake operating member 33 may be another member such as a lever or a switch. The brake valve 26 supplies hydraulic oil to the hydraulic brakes 21, 22 in response to operation of the brake operating member 33.

[0020] The brake charge valve 25 includes a pump flow path 34, a charge flow path 35, a check valve 36, a priority spool 37, an electromagnetic proportional pilot relief valve 38, and a reverse shuttle valve 39. The pump flow path 34 is connected to the hydraulic pump 23. The charge flow path 35 is connected to the brake valve 26. The check valve 36 is disposed between the pump flow path 34 and the charge flow path 35. The check valve 36 allows hydraulic oil to flow from the pump flow path 34 to the charge flow path 35 and restricts the flow of hydraulic oil from the charge flow path 35 to the pump flow path 34.

[0021] The priority spool 37 is connected to the pump flow path 34. The priority spool 37 controls the brake pump pressure. The electromagnetic proportional pilot relief valve 38 controls the priority spool 37 in response to a command signal from the controller 29. As a result, the brake charge valve 25 controls the brake pump pressure in response to the command signal from the controller 29.

[0022] The reverse shuttle valve 39 is connected to the charge flow path 35. The reverse shuttle valve 39 is connected to the first brake drive circuit 31 and the second brake drive circuit 32. The reverse shuttle valve 39 distributes the hydraulic oil from the charge flow path 35 to the hydraulic pressure of the first brake drive circuit 31 and the second brake drive circuit 32 so that the brake charge pressure of the first accumulator 27 and the brake charge pressure of the second accumulator 28 are equalized.

[0023] A first relief valve 41 and a second relief valve 42 are connected to the pump flow path 34. The first relief valve 41 connects the pump flow path 34 to a drain flow path 43 when the hydraulic pressure in the pump flow path 34 becomes excessive, thereby preventing the brake pump pressure in the pump flow path 34 from becoming excessive. The second relief valve 42 connects the pump flow path 34 to the drain flow path 43 when the hydraulic pressure in the pump flow path 34 becomes maximum during brake charging, thereby preventing the brake charge pressure in the charge flow path 35 from becoming excessive during brake charging.

[0024] A fan motor 44 is connected to the brake charge valve 25. The fan motor 44 is a hydraulic motor. A cooling fan 45 is connected to the fan motor 44 to cool the cooling water of the engine 18 or the hydraulic oil in the hydraulic circuit 24. The fan motor 44 is driven by the hydraulic oil supplied from the hydraulic pump 23 via the brake charge valve 25. This causes the cooling fan 45 to rotate.

[0025] 3 is an enlarged view of a portion of the configuration of the brake charge valve 25. The priority spool 37 includes a first pilot port 51 and a second pilot port 52. The brake charge valve 25 includes a first pilot circuit 53 and a second pilot circuit 54. The first pilot circuit 53 is connected to the pump flow path 34 via a pressure compensating flow valve 55. The first pilot circuit 53 is connected to the pump flow path 34 between the priority spool 37 and the check valve 36. The first pilot circuit 53 is connected to the first pilot port 51 of the priority spool 37.

[0026] The second pilot circuit 54 is connected to the pump flow path 34 between the priority spool 37 and the check valve 36. The second pilot circuit 54 is connected to a second pilot port 52 of the priority spool 37. Brake pump pressure is applied to the second pilot port 52 via the second pilot circuit 54.

[0027] The electromagnetic proportional pilot relief valve 38 is connected to a first pilot circuit 53. The electromagnetic proportional pilot relief valve 38 controls the pilot pressure applied to a first pilot port 51 of the priority spool 37 via the first pilot circuit 53. The electromagnetic proportional pilot relief valve 38 controls the pilot pressure to the first pilot port 51 in response to a command signal from the controller 29. As a result, the brake charge valve 25 controls the brake pump pressure in response to the command signal from the controller 29.

[0028] The priority spool 37 is movable among a charge position Pc, a neutral position Pn, and a drain position Pd. A spring 56 is connected to the priority spool 37. The balance between the resultant force of the pilot pressure to the first pilot port 51 and the biasing force of the spring 56 and the brake pump pressure to the second pilot port 52 causes the priority spool 37 to move among the charge position Pc, the neutral position Pn, and the drain position Pd.

[0029] At the charge position Pc, the priority spool 37 allows hydraulic oil from the hydraulic pump 23 to flow to the pump flow path 34 but not to the fan motor 44. At the neutral position Pn, the priority spool 37 allows hydraulic oil from the hydraulic pump 23 to flow to both the pump flow path 34 and the fan motor 44. At the drain position Pd, the priority spool 37 allows hydraulic oil from the hydraulic pump 23 to flow to the fan motor 44 and connects the pump flow path 34 to the drain flow path 43.

[0030] The resultant force of the pilot pressure to the first pilot port 51 and the biasing force of the spring 56 determines the target pressure of the brake pump pressure. When the brake pump pressure is lower than the target pressure, the priority spool 37 is set to the charge position Pc. This increases the brake pump pressure so that it reaches the target pressure. When the brake pump pressure is higher than the target pressure, the priority spool 37 is set to the drain position Pd. This decreases the brake pump pressure so that it reaches the target pressure. When the brake pump pressure matches the target pressure, the priority spool 37 is set to the neutral position Pn.

[0031] As shown in FIG. 2, the work machine 1 is equipped with a rotational speed sensor 57, an oil temperature sensor 58, and oil pressure sensors 59, 60. The rotational speed sensor 57 detects the engine rotational speed of the engine 18. The rotational speed sensor 57 outputs a signal indicating the engine rotational speed. The oil temperature sensor 58 detects the temperature of the hydraulic oil (hereinafter referred to as "oil temperature"). The oil temperature sensor 58 outputs a signal indicating the oil temperature. The oil pressure sensors 59, 60 detect the brake charge pressure of the accumulators 27, 28. The oil pressure sensors 59, 60 output a signal indicating the brake charge pressure.

[0032] The work machine 1 is equipped with a starter motor 61 and a start switch 62. The starter motor 61 starts the engine 18. The start switch 62 can be operated by an operator to start the engine 18. When the start switch 62 is operated, the starter motor 61 is actuated to start the engine 18. The start switch 62 outputs a signal indicating that the start switch 62 has been operated.

[0033] The controller 29 includes a processor such as a CPU and memories such as RAM and ROM. The controller 29 stores programs and data for controlling the work machine 1, and controls the work machine 1 based on the programs and data. The controller 29 receives signals from the sensors 57-60 and the start switch 62 described above.

[0034] The controller 29 outputs a command signal to the above-described brake charge valve 25 to electrically control the brake charge valve 25. The controller 29 controls the brake pump pressure by controlling the brake charge valve 25. In this way, the controller 29 controls the brake charge pressure.

[0035] FIG. 4 is a diagram showing the characteristics of the brake charge valve 25. More specifically, FIG. 4 shows the characteristics of the electromagnetic proportional pilot relief valve 38. In FIG. 4, the horizontal axis represents the current value of the command signal from the controller 29, and the vertical axis represents the target pressure of the brake pump pressure. As shown in FIG. 4, the smaller the current value of the command signal, the higher the target pressure of the brake pump pressure. That is, the smaller the current value of the command signal, the more the electromagnetic proportional pilot relief valve 38 increases the pilot pressure to the first pilot port 51 of the priority spool 37. As a result, the target pressure of the brake pump pressure, which is determined by the resultant force of the pilot pressure to the first pilot port 51 and the biasing force of the spring 56, increases. The controller 29 increases or decreases the target pressure of the brake pump pressure by outputting a command signal to the electromagnetic proportional pilot relief valve 38. The control of the brake charge pressure performed by the controller 29 will now be described.

[0036] Controller 29 selectively executes normal charge control and start assist control. Normal charge control is brake charge pressure control that is executed in a normal state after engine 18 has started and the engine rotation speed has reached a predetermined rotation speed threshold. In normal charge control, controller 29 controls brake charge valve 25 so that the brake pump pressure becomes a predetermined first pressure P1.

[0037] The starting assist control is a control of the brake charge pressure that is executed after the engine 18 has started and until the engine rotation speed reaches a rotation speed threshold. During the starting assist control, the controller 29 controls the brake charge valve 25 so that the brake pump pressure becomes a second pressure P2. The second pressure P2 is smaller than the first pressure P1. The second pressure P2 is equal to or greater than the minimum hydraulic pressure for operating the hydraulic brake.

[0038] Fig. 5 is a flowchart showing the process of controlling brake charge pressure. After the start of the engine 18 is initiated by the start switch 62, the controller 29 determines whether to execute start assist control through the process shown in Fig. 5. As shown in Fig. 5, in step S101, the controller 29 acquires the oil temperature Tm1. The controller 29 acquires the oil temperature Tm1 based on a signal from the oil temperature sensor 58.

[0039] In step S102, the controller 29 determines whether the oil temperature Tm1 is lower than a predetermined temperature threshold value Th1. If the oil temperature Tm1 is lower than the temperature threshold value Th1, in step S103, the controller 29 executes start assist control. In the start assist control, the controller 29 controls the brake charge valve 25 so that the brake pump pressure becomes a second pressure P2 that is lower than the first pressure P1. In detail, as shown in FIG. 4, the controller 29 outputs a command signal of a current value A2 to the brake charge valve 25 such that the target pressure becomes the second pressure P2.

[0040] In step S104, the controller 29 acquires the engine rotation speed Ne. The controller 29 acquires the engine rotation speed Ne from a signal from the rotation speed sensor 57. In step S105, the controller 29 determines whether the engine rotation speed Ne is equal to or greater than a rotation speed threshold value Th2. The rotation speed threshold value Th2 is, for example, the idling rotation speed of the engine 18. If the engine rotation speed Ne is lower than the rotation speed threshold value Th2, the controller 29 maintains the start assist control in step S103. That is, after the engine 18 starts, the controller 29 executes the start assist control until the engine rotation speed Ne reaches the rotation speed threshold value Th2.

[0041] When the engine rotation speed Ne reaches or exceeds the rotation speed threshold value Th2, the controller 29 ends the start assist control and executes normal charge control in step S106. In the normal charge control, the controller 29 controls the brake charge valve 25 so that the brake pump pressure becomes the first pressure P1. In detail, as shown in Fig. 4, the controller 29 outputs a command signal of a current value A1 to the brake charge valve 25 so that the target pressure becomes the first pressure P1.

[0042] If the oil temperature Tm1 is equal to or higher than the temperature threshold value Th1 in step S102, the controller 29 does not execute the start assist control, and executes the normal charge control in step S106. That is, if the oil temperature Tm1 is equal to or higher than the temperature threshold value Th1 when the engine 29 is started, the controller 29 controls the brake charge pressure using the normal charge control.

[0043] In step S107, the controller 29 acquires the brake charge pressure Pb. The controller 29 acquires the brake charge pressure Pb from signals from the hydraulic sensors 59, 60. In step S108, the controller 29 determines whether the brake charge pressure Pb is equal to or greater than the first pressure P1. If the brake charge pressure Pb is less than the first pressure P1, the controller 29 maintains the normal charge control in step S106. That is, the controller 29 maintains the normal charge control until the brake charge pressure Pb reaches the first pressure P1, which is the target pressure for the normal charge control.

[0044] When the brake charge pressure Pb reaches or exceeds the first pressure P1, the controller 29 ends the normal charge control in step S109. In this case, the controller 29 controls the brake charge valve 25 so that the brake pump pressure becomes a third pressure that is lower than the first pressure P1. Thereafter, when the brake charge pressure Pb becomes lower than a predetermined recharge pressure, the controller 29 resumes the normal charge control, thereby increasing the brake charge pressure Pb to the first pressure P1. The recharge pressure is a pressure that is equal to or lower than the first pressure P1.

[0045] 6 is a timing chart showing the control of the brake charge pressure. As shown in FIG. 6, at time T0, the signal from the start switch 62 is off and the engine 18 is stopped.

[0046] At time T1, when the start switch 62 is operated, an ON signal is output from the start switch 62. This activates the starter motor 61, and starts the engine 18. After time T1, while the ON signal is being output, the starter motor 61 continues to operate, which gradually increases the engine rotation speed.

[0047] At time T1, if the oil temperature is lower than temperature threshold value Th1, controller 29 executes start assist control. In the start assist control, controller 29 controls brake charge valve 25 so that the target pressure of the brake pump pressure becomes second pressure P2. Therefore, the brake pump pressure and brake charge pressure are suppressed to second pressure P2. This reduces the load torque of hydraulic pump 23, and the engine rotation speed increases smoothly from time T1 to time T2.

[0048] When the engine rotation speed reaches the rotation speed threshold value Th2 at time T2, the controller 29 ends the start assist control and executes normal charge control. In the normal charge control, the controller 29 controls the brake charge valve 25 so that the target pressure of the brake pump pressure becomes the first pressure P1. This increases the brake pump pressure, and after time T2, the brake charge pressure increases rapidly.

[0049] At time T3, when the brake charge pressure reaches the first pressure P1, the controller 29 ends the normal charge control and reduces the target pressure of the brake pump pressure to the third pressure P3. Note that in FIG. 6, the third pressure P3 is the same as the second pressure P2. However, the third pressure P3 may be smaller than the second pressure P2. Alternatively, the third pressure P3 may be a value between the first pressure P1 and the second pressure P2.

[0050] In the work machine 1 according to the present embodiment described above, when the engine 18 is started, the brake pump pressure is suppressed to a second pressure P2, which is lower than the first pressure P1 during normal charge control, by start assist control. As a result, the load torque from the hydraulic pump 23 is reduced when the engine 18 is started. This allows the engine 18 in the work machine 1 to be started smoothly.

[0051] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the gist of the invention.

[0052] The work machine 1 is not limited to a wheel loader, but may be other machines such as a grader or a dump truck. The configuration of the work machine 1 is not limited to that of the above embodiment and may be modified. For example, the power source is not limited to an internal combustion engine, but may be an electric motor.

[0053] The configuration of the drive system for the hydraulic brakes 21, 22 is not limited to that of the above embodiment and may be modified. For example, the fan motor 44 may be omitted. The configuration of the brake charge valve 25 is not limited to that of the above embodiment and may be modified. For example, the priority spool 37, the electromagnetic proportional pilot relief valve 38, and the reverse shuttle valve 39 may be separate components.

[0054] The process of controlling the brake charge pressure is not limited to that of the above embodiment and may be modified. For example, the controller 29 may execute the start assist control until a predetermined time has elapsed after the engine 18 has started to start. The controller 29 may terminate the start assist control and execute normal charge control when the predetermined time has elapsed after the engine 18 has started to start. [Industrial Applicability]

[0055] According to the present disclosure, the power source can be started smoothly in a work machine. [Explanation of symbols]

[0056] 18: Engine (power source), 21, 22: Hydraulic brake, 23: Hydraulic pump, 24: Hydraulic circuit, 25: Brake charge valve, 26: Brake valve, 27, 28: Accumulator, 29: Controller, 57: Rotational speed sensor, 58: Oil temperature sensor, 59, 60: Oil pressure sensor

Claims

1. A power source and a hydraulic pump driven by the power source; a hydraulic brake that generates a braking force by the hydraulic oil discharged from the hydraulic pump; a brake charge valve for controlling a brake pump pressure that indicates the hydraulic pressure of the hydraulic fluid discharged from the hydraulic pump; a controller that executes normal charge control to control the brake charge valve so that the brake pump pressure becomes a predetermined first pressure; Equipped with When starting the engine, a start assist control is executed to control the brake charge valve so that the brake pump pressure becomes a second pressure lower than the first pressure. Work machinery.

2. An oil temperature sensor is further provided to detect the temperature of the hydraulic oil. The controller Acquire the temperature of the hydraulic oil; When the temperature of the hydraulic oil is lower than a predetermined temperature threshold at the time of starting the engine, the start assist control is executed.

2. The work machine according to claim 1.

3. When the temperature of the hydraulic oil is equal to or higher than the temperature threshold value at the time of starting the engine, the controller does not execute the start assist control and executes the normal charge control.

3. The work machine according to claim 2.

4. a rotational speed sensor for detecting a rotational speed of the power source; The controller acquiring a rotational speed of the driving source; After the engine is started, the start assist control is executed until the rotation speed of the drive source reaches a predetermined rotation speed threshold.

2. The work machine according to claim 1.

5. When the rotation speed of the driving source reaches the rotation speed threshold value after the engine is started, the controller terminates the start assist control and executes the normal charge control.

5. The work machine according to claim 4.

6. the power source is an engine, The rotational speed threshold is an idling rotational speed of the engine.

6. A work machine according to claim 5.

7. a hydraulic circuit connecting the hydraulic pump and the hydraulic brake; a brake valve disposed in the hydraulic circuit between the hydraulic pump and the hydraulic brake; an accumulator connected to the hydraulic circuit; Furthermore, the brake charge valve is disposed in the hydraulic circuit between the hydraulic pump and the brake valve; The accumulator is connected to the hydraulic circuit between the brake charge valve and the brake valve.

2. The work machine according to claim 1.

8. a hydraulic pressure sensor for detecting a brake charge pressure indicating the hydraulic pressure of the hydraulic fluid in the accumulator; The controller After the engine is started, the start assist control is executed until the rotation speed of the drive source reaches a predetermined rotation speed threshold value; After the engine is started, if the rotation speed of the drive source reaches the rotation speed threshold value, the start assist control is terminated and the normal charge control is executed; The brake charge pressure is acquired; When the brake charge pressure becomes equal to or greater than a predetermined pressure threshold, the normal charge control is terminated, and the brake charge valve is controlled so that the brake pump pressure becomes a third pressure that is lower than the first pressure.

8. The work machine according to claim 7.

9. the second pressure is equal to or greater than a minimum hydraulic pressure for actuating the hydraulic brake; 2. The work machine according to claim 1.

10. A method for controlling a work machine including a power source, a hydraulic pump driven by the power source, a hydraulic brake that generates a braking force by hydraulic oil discharged from the hydraulic pump, and a brake charge valve that controls a brake pump pressure that indicates a hydraulic pressure of the hydraulic oil discharged from the hydraulic pump, the method comprising: performing normal charge control to control the brake charge valve so that the brake pump pressure becomes a predetermined first pressure; When starting the engine, a start assist control is executed to control the brake charge valve so that the brake pump pressure becomes a second pressure lower than the first pressure. A method for providing the above.

11. Obtaining the temperature of the hydraulic oil; When the temperature of the hydraulic oil is lower than a predetermined temperature threshold at the time of starting the engine, the start assist control is executed. The method of claim 10 comprising:

12. When the temperature of the hydraulic oil is equal to or higher than the temperature threshold value at the time of starting the engine, the start assist control is not executed, and the normal charge control is executed. The method of claim 11 , comprising:

13. acquiring a rotation speed of the driving source; After the engine is started, the start assist control is executed until the rotation speed of the drive source reaches a predetermined rotation speed threshold value. The method of claim 10 comprising:

14. When the rotation speed of the driving source reaches the rotation speed threshold value after the engine is started, the start assist control is terminated and the normal charge control is executed. The method of claim 13 comprising:

15. the power source is an engine, The rotational speed threshold is an idling rotational speed of the engine. The method of claim 13.

16. The work machine includes: a hydraulic circuit connecting the hydraulic pump and the hydraulic brake; a brake valve disposed in the hydraulic circuit between the hydraulic pump and the hydraulic brake; an accumulator connected to the hydraulic circuit; Furthermore, the brake charge valve is disposed in the hydraulic circuit between the hydraulic pump and the brake valve; The accumulator is connected to the hydraulic circuit between the brake charge valve and the brake valve. The method of claim 10.

17. After the engine is started, the start assist control is executed until the rotation speed of the drive source reaches a predetermined rotation speed threshold value; When the rotation speed of the driving source reaches the rotation speed threshold value after the engine is started, the start assist control is terminated and the normal charge control is executed. detecting a brake charge pressure indicative of hydraulic fluid pressure in the accumulator; When the brake charge pressure becomes equal to or greater than a predetermined pressure threshold, the normal charge control is terminated, and the brake charge valve is controlled so that the brake pump pressure becomes a third pressure that is lower than the first pressure.

17. The method of claim 16, comprising:

18. the second pressure is equal to or greater than a minimum hydraulic pressure for actuating the hydraulic brake; The method of claim 10.

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